In recent years, recording density of magnetic memory media has been remarkably increasing. For example, the surface recording density of a hard disk drive unit has been doubling each year, and it is considered that the spin valve type magnetoresistive effect head currently in use will reach the limit of its reproduction capability in the near future. Therefore, it is necessary to develop a magnetic effect element with higher sensitivity, which can form a magnetic head.
In a situation like this, the tunnel type magnetoresistive effect type head (TMR head) is considered indispensable as a promising candidate for a next-generation leading head, where a recording density of 100 Gbit/square inch is to be realized. The TMR head can provide a high MR ratio (40% or higher), and a reproduction output that is several times as high as the existing spin valve type magnetoresistive effect head (SVMR head), etc.
Although there are trial production reports concerning TMR heads from a plurality of companies, the surface recording density of the TMR head has not yet reached a satisfactory level according to these reports. The TMR elements that have been made so far have junction resistance values ranging between approximately 20 and 40 Ω/μm2, and MR ratios ranging between approximately 7 and 20%, which are not satisfactory to realize a magnetoresistive element that fully utilizes the real strength of a TMR element.
Further, since the junction area of the TMR element to be included in a magnetic head becomes smaller as the surface recording density of a magnetic record reproducing apparatus becomes higher, if junction resistance of a TMR element stays as it is at the present, the resistance of the magnetic head becomes greater rapidly. Because of this, problems arise, such as degradation of S/N, an increase in delay, etc., and accurate operations of the magnetic head become difficult.